[Federal Register Volume 65, Number 171 (Friday, September 1, 2000)]
[Notices]
[Pages 53338-53340]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-22541]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

[Policy Statement Number ACE-00-23.901(d)(2)]


Proposed Issuance of Policy Memorandum, Notice of Compliance With 
the Engine Ingestion Requirements Applicable to Turbine Powered, Part 
23, Normal, Utility, Acrobatic, and Commuter Category Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of policy statement; request for comments.

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SUMMARY: This document proposes to adopt new policy for compliance with 
the engine ingestion requirements applicable to turbine powered, 
normal, utility, acrobatic, and commuter category airplanes.

DATES: Comments submitted must be received no later than October 2, 
2000.

ADDRESSES: Send all comments on this proposed policy statement to the 
individual identified under FOR FURTHER INFORMATION CONTACT.

FOR FURTHER INFORMATION CONTACT: Randy Griffith, Federal Aviation 
Administration, Small Airplane Directorate, Regulations and Policy 
Branch, ACE-111, 901 Locust, Room 301, Kansas City, Missouri 64106;

[[Page 53339]]

telephone (816) 329-4126; fax (816) 329-4090; email: 
[email protected]>.

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite your comments on this proposed policy statement, ACE-00-
23.901(d)(2). You may submit whatever written data, views, or arguments 
you choose. You should mark your comments, ``Comments to policy 
statement ACE-00-23.901(d)(2),'' and submit in duplicate to the above 
address. We will consider all comments received on or before the 
closing date. We may change the proposals contained in this notice in 
light of the comments received.
    You may also send comments via the Internet using the following 
address: [email protected]. Comments sent via fax or the Internet 
must contain ``Comments to policy statement ACE-00-23.901(d)(2)'' in 
the subject line. You do not need to submit in duplicate. Writers 
should format in Microsoft Word 97 or ASCII any file attachments that 
are sent via the Internet.
    Submit comments using the following format:
     Organize comments issue-by-issue. For example, discuss a 
comment concerning design evaluation and a comment about maintenance as 
two separate issues.
     For each issue, state what specific change you are 
requesting to the proposed policy memorandum.
     Include justification (for example, reasons or data) for 
each request.

The Proposed Policy

Background

    The current Sec. 23.901(d)(2) requirement was incorporated by 
Amendment 23-53. However, the basic requirement, which has evolved into 
the current Sec. 23.901(d)(2), was incorporated by Amendment 23-18.
    Amendment 23-18 required that the engine installation provide 
continued engine operation without a sustained loss of power when 
operated at flight idle in rain for at least three minutes. The rate of 
rain ingestion was to be not less than 4 percent, by weight, of the 
engine induction airflow rate. The rule was incorporated due to reports 
of turbine engine power loss while operating in heavy rain. The intent 
of the rule was twofold: (1) To ensure that installation effects do not 
result in deterioration of the engine's rain ingestion tolerance 
determined by engine certification, and (2) to evaluate the engine's 
capability for rain ingestion for engines that were certificated before 
Amendment 33-6 since rain ingestion requirements were not added to 14 
CFR part 33 until Amendment 33-6. Therefore, the rate of rain ingestion 
to be considered was based upon the part 33 engine certification 
requirement at the time.

Revisions of Standards

    Amendment 23-29 revised the requirement to consider rated takeoff 
power/thrust. Also, the preamble to Amendment 23-29 further defined the 
intent of Sec. 23.901(d)(2) by specifically stating that the rule is to 
ensure that installation effects do not result in any deterioration of 
the powerplant rain ingestion tolerance. Therefore, compliance with 
Sec. 23.901(d)(2) required a separate determination for engine 
installation other than the requirements addressed by part 33 (for 
example, engine certification without further installation 
certification is inadequate to demonstrate compliance with the part 23 
requirement).
    Amendment 23-43 added a requirement that the installation be 
evaluated at the maximum installed power/thrust for takeoff. This new 
requirement was due to engine installations where rated takeoff power 
could be less than installed takeoff power; for example, de-rate 
thrust. The amendment also added a requirement that the engine be 
accelerated and decelerated safely under the rain conditions; however, 
Amendment 23-51 removed this consideration.
    Amendment 23-53 added the current rule. The current amendment 
requires the installed engine to withstand ingestion of rain, hail, 
ice, and birds at a level not less than that established under engine 
certification. The significant changes with the new rule include 
operating concerns other than loss of power (for example, engine 
surges), the addition of hail, ice, and bird ingestion requirements, 
and replacement of specific rain quantification with the conditions 
used during engine certification. Under Amendment 23-53, the airplane 
applicant needs to evaluate the conditions used to address rain, hail, 
ice, and bird ingestion during engine certification and how the 
installation relates to these conditions.

Means of Compliance

    When showing compliance with the rain ingestion requirements for 
all amendment levels of Sec. 23.901(d)(2), compliance is typically 
accomplished with design analysis that identifies areas of concern and 
test. Items that you should consider when evaluating the installation 
include: Areas where water pooling (for example, inlet system channels, 
indentations, and so forth, typical of turbopropeller type inlets) or 
water shed (for example, wings directing water into the inlet system 
typical of engines mounted behind the wings) may occur. Areas such as 
these could cause localized ``slugs'' of water ingestion that would not 
normally be addressed during engine certification. Also, since the rain 
ingestion requirements in part 33 were not added until Amendment 33-6, 
the airplane applicant needs to evaluate the engine's certification 
basis to determine if the engine has been subjected to part 33 rain 
ingestion testing. If the engine does not have Amendment 33-6 or a 
subsequent amendment as part of the certification basis, in accordance 
with Sec. 23.903(a)(2)(iii), the engine must have a safe service 
history of rain ingestion in similar installations.
    Although testing is typically performed, if design analysis shows 
that the installation will not affect the water ingestion 
characteristics, appropriately substantiated design analysis may be 
adequate to demonstrate rain ingestion compliance. Proof could include, 
or be a combination of, items such as data from rig tests, previous 
tests by the applicant on a similar installation, service experience by 
the applicant on a similar installation, or representative 
developmental tests, and so forth.
    If it is determined that testing for rain ingestion is required, 
flight test is not required. The intent of the part 23 rule is to 
ensure that the engine installation has the same rain ingestion 
tolerance as the certificated engine. Since a ground static engine test 
normally demonstrates engine certification compliance, use of 
installation ground tests at the required power/thrust settings has 
been the normally accepted means of compliance. You can use design 
analysis to determine critical configurations and conditions of the 
installation; possibly reducing required installation tests to those 
critical configurations and conditions instead of repeating the entire 
part 33 test conditions. Engine certification should address the 
results of the critical point analysis for the engine with the scope of 
required installation testing possibly influenced by this analysis. 
Therefore, it is important for the engine installer to research the 
conditions and requirements used for engine certification.

Other Considerations for Compliance

    Amendment 23-53 also added requirements for ice, hail, and birds. 
Examples of installation issues normally not addressed by engine 
certification,

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but which should be addressed for installation compliance, include the 
following: Ice build-up on areas where ice shed may be ingested by the 
engines (for example, ice shed from wings into aft mounted engines) and 
consideration of items such as inlet splitters, acoustic liners, and so 
forth, that may be damaged by impact with ice, hail, and birds.

    Issued in Kansas City, Missouri on August 16, 2000.
Michael Gallagher,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 00-22541 Filed 8-31-00; 8:45 am]
BILLING CODE 4910-13-P